1. Technical Field
The present disclosure relates to a method of estimating inter-carrier interference (ICI) and an ICI mitigating equalizer and, more particularly, to a method of estimating an ICI component by approximating a channel to an (M1)-th order model and an ICI mitigating equalizer.
2. Discussion of Related Art
Orthogonal frequency division multiplexing (OFDM) systems are applied to various broadcasting/communication systems. An OFDM system serves to transmit data by using a plurality of sub-carriers that are orthogonal to one another.
FIG. 1 illustrates examples of an OFDM transmitter 110 and an OFDM receiver 120 in an OFDM system.
Referring to FIG. 1, the OFDM transmitter 110 includes an encoder 11, a mapper 112, an inverse fast Fourier transform (IFFT) block 113, a cyclic prefix (CP) insertion unit 114, a radio frequency (RF) transmitter 115, and a transmitting antenna 116. The OFDM receiver 120 includes a receiving antenna 121, an RF receiver 122, a CP remover 123, a fast Fourier transform (FFT) block 124 an equalizer 125, a demapper 126, and a decoder 127.
In the OFDM transmitter 110, a cyclic prefix (CP) is inserted into a transmitted signal that is transformed through IFFT so as to prevent inter-symbol interference (ISI) and to estimate a channel. The transmitted signal Si(n) into which the CP is inserted is output to a wired/wireless channel via the RF transmitter 115 and the transmitting antenna 116. In the OFDM receiver 120, a received signal ri(n) from which the CP is removed is transformed into a received signal Ri(k) in a frequency domain by using the FFT block 124. The equalizer 125 outputs a transmitting signal Ŝi(k) estimated by equalizing the received signal Ri(k) in the frequency domain.
In order to accurately estimate the transmitted signal by using the OFDM receiver 120, a response characteristic of a channel has to be accurately recognized. The response characteristic of the channel may be changed according to time, however due to time-selectivity. The response characteristic of the channel may be changed according to frequency due to frequency-selectivity. Accordingly, it is difficult to accurately recognize the response characteristic of the channel. On the other hand, the time-selectivity and the frequency-selectivity of a channel damages orthogonality among sub-carriers and causes inter-carrier interference (ICI). Although the response characteristic of the channel may be accurately recognized by using pilots included in the CP, it may be inaccurate to estimate the transmitted signal due to an influence of the ICI.
The ICI increases the complexity of the accurate estimation of the transmitted signal by using the OFDM receiver 120. In order to allow the OFDM receiver 120 to accurately estimate the transmitted signal, the ICI component included in the received signal is initially estimated, and the ICI component included in the received signal has to be removed or mitigated based on the estimation result. Because a calculation amount and computational complexity increase in order to remove or mitigate the ICI component included in the received signal, the structure of the OFDM receiver 120 becomes complex. The OFDM receiver 120 is designed in consideration of a trade-off relation between accuracy of estimation and computational complexity.